The Wonder Weeks app represents a digital adaptation of the pioneering developmental research conducted since 1971, originally observing chimpanzees in Tanzania before being applied to human infant development. This Android application serves as a comprehensive guide to the ten mental developmental leaps that occur during a baby's first 20 months, providing parents with explanations for behavioral changes and practical support strategies. The core functionality centers around a detailed leap calendar that predicts when babies will experience developmental transitions, accompanied by explanations of what cognitive changes are occurring. Each leap includes descriptions of typical behaviors parents might observe, along with suggested games and activities tailored to the baby's current developmental stage. The app features daily updates, milestone tracking, and personalized content based on the baby's exact age and leap progression. User experience varies significantly according to device compatibility and recent updates. The interface employs a clean, minimalist design with intuitive navigation through leap timelines and development articles. However, technical stability has been inconsistent, with multiple users reporting crashes and loading issues following updates. When functioning properly, the app provides valuable real-time guidance for parents dealing with fussy periods or sleep regression episodes. User feedback reveals a pattern of technical issues affecting the overall experience. Rebecca Markus (December 2024) reported payment issues followed by app crashes, though noted resolution after updates. Hannah Wood (December 2024) experienced similar loading problems despite premium payment, while Katelyn Bennett (March 2025) documented purchase restoration difficulties that were eventually resolved through developer support. Positive reviews from users like Nihaad Wilkinson (December 2024) highlight the app's effectiveness in helping first-time parents understand developmental changes and maintain confidence during challenging phases. The application demonstrates significant value when operational, offering research-backed insights that help parents interpret infant behavior through a developmental lens. Primary limitations involve technical reliability and restoration issues for previous purchasers. The $60 premium access cost represents a substantial investment that may not deliver consistent value across all devices. Ideal usage involves cross-referencing app predictions with professional pediatric advice rather than relying exclusively on its recommendations.